1. Field of the Invention
The present invention relates to a remotely controlled power disconnect circuit which provides a ground fault and prevents power from being applied to an electrical outlet in the event the electrical neutral is lost, the load is shorted, or some other unsafe condition arises.
2. Description of the Prior Art
In prior art electrical power systems for a dwelling, 120 VAC or 240 VAC power is supplied to the electrical outlets arranged throughout the home. The load on respective circuits including one or more outlets is monitored at a junction box, and a relay is "tripped" so as to disconnect the power to the circuit in the event that an excessive current is drawn by the circuit. Such an excessive current is drawn, for example, when there is a short in a device plugged into an outlet or too many appliances are connected to the circuit. The "tripping" of the relay prevents further supply of electrical power to the circuit so as to prevent perpetuation of the unsafe condition by causing a fire or an electrical shock.
A power disconnect circuit of the type just described may be depicted in simplified form as shown in FIGURE 1. In particular, a ground fault detector, which may comprise a transformer coil, may be used to detect external impedances applied to the power line circuit connected to a particular relay at the junction box, and as described above, application of power to the circuit may be controlled remotely by opening the relay to disconnect the "hot" line when excessive impedances are measured. In other words, the relay is closed during normal operation (i.e., as long as a large external impedance is not detected), but when a large external impedance is detected, the relay is opened so as to shut-off power supply to the circuit. Such a technique is known as universal ground fault protection.
Such a system functions quite well in typical dwellings as long as a large external impedance or ground fault on a particular circuit may be detected by the ground fault detector. However, such a system does not prevent the 120 VAC power from being applied to unused outlets unless the whole power circuit is disconnected. As a result, instances of electric shock may still occur as when a child sticks a metal object such as a fork into an electrical outlet, for example. Accordingly, the prior art arrangement is potentially dangerous.